But the leadership of the group, EKIN, which describes itself as a grassroots co-ordinator of Basque pro-independence groups, said the state had in effect outlawed all organisations for Basque independence.

Some 300 officers were involved in the operation, which took place in the northern Basque region, the neighbouring region of Navarra and in Madrid.

Police said those arrested would be charged with being members of an armed group.

Raids denounced

Two of the suspects are members of Herri Batasuna - which contests elections under the name Euskal Herritarrok and is widely considered ETA's political wing.

The leadership of EKIN said police searches of Herri Batasuna had merely yielded lists of activists, a computer and discs, personnel agendas, calendars and $13,000 in cash.

A number of Basque nationalist politicians criticised the raids on the offices of a political party.

The spokesman of the separatist Euskal Herritarok party, Arnaldo Otegi, described the operation as an attempt to outlaw all organisations of the Basque independence movement.

Legal moves

And Rafa Larreina of the Eusko Alkartasuna party, which condemns ETA violence, said of the raids on the Herri Batasuna's offices; "It's disturbing, from a democratic point of view, that they search headquarters of legal political parties"

France on Wednesday extradited to Spain, a suspected member ETA, Francisco Javier Chimeno Inza, accused of plotting to assassinate King Juan Carlos in 1995.

About 800 people have been killed since the organisation launched its campaign for an independent homeland more than 30 years ago.

The government has proposed a tightening of Spain's anti-terrorism laws to include a wider interpretation of the crime "apology for terrorism" - which could mean that anyone advocating independence for the Basque country is in danger of arrest.